A cellular phone and an IP phone are often used in a place where ambient noise is large. Accordingly, it is necessary for the communication terminals to adjust a reception sound in consideration for a usage environment of the user (more to the point, ambient noise). As a technique for adjusting the reception sound, there are a technique for varying the sound amount of the reception sound (AGC: Auto Gain Control) and a technique for emphasizing a formant of the reception sound.
However, listenability of the reception sound depends on auditory property of the user. Consequently, it is not necessary the case that uniform variation of the sound volume of the reception sound in accordance with an ambient noise enables the user to hear well. That is, in a conventional communication terminal, it is impossible to adjust the reception sound only when the user feels that it is hard to hear.
Japanese Laid-open Patent Publication No. 04-328798, Japanese Laid-open Patent Publication No. 2002-185572, and Japanese Laid-open Patent Publication No. 2004-165865 disclose techniques for adjusting the reception sound in the communication apparatus.